Introduction

The Florida Exotic Pest Plant Council's (FLEPPC) 2013 List of Invasive Plant Species includes two Category I and two Category II Solanum species (Solanaceae) (FLEPPC 2007). Category I Solanum species identified by the Council are S. tampicense Dunal (wetland nightshade, aquatic soda apple) and S. viarum Dunal (tropical soda apple). Category II Solanum species identified by the Council are S. diphyllum L. (twoleaf nightshade) and S. torvum Sw. (turkeyberry). Solanum jamaicense Mill. (Jamaican nightshade), included in Category II in the 2009 FLEPPC list, was removed in 2011 because of a lack of occurrence data in natural areas.

Category I invasive exotics are defined by the FLEPPC as those plants that alter native plant communities by displacing native species, changing community structure or ecological functions, or hybridizing with natives. The FLEPPC defines Category II invasive exotics as those that have increased in abundance or frequency, but have not yet altered Florida plant communities to the extent shown by Category I species.

As members of the same genus, the Solanum species identified by the FLEPPC as invasive share certain morphological features. These similarities can lead to misidentification. This publication provides a guide to differentiate the invasive Solanum species, along with information about the ecology and management of each species. We have also included information on Jamaican nightshade and another relatively common species, Solanum capsicoides All. (red soda apple), both of which can easily be confused with some of the invasive Solanum species.

Identification and Florida Distribution

The four Solanum spp. on the FLEPPC's 2013 list and the two other species mentioned above can be identified using morphological characters and also by the habitat in which they are found. For example, wetland nightshade (S. tampicense) is found in wetlands, whereas the other four species are typically found in more upland and often disturbed, habitats. Tropical soda apple is found both in open areas with full sun (often in pastures) but also in wooded hammocks. In contrast, Jamaican nightshade is found almost exclusively in or nearby wooded areas.

The following table provides some of the key characters that can be used to differentiate the species, as well as information on the habitats in which the species are found and the counties where herbaria specimens have been collected.

Native Distribution

The four Solanum spp. on the FLEPPC 2013 list, along with Jamaican nightshade, are native to Mexico, Central America, South America, and/or the Caribbean.

Experts do not agree on the native range of S. capsicoides. Some consider the plant to be a native in Florida (Wunderlin and Hansen 2008) while others believe it is native to the Caribbean (D’Arcy 1974) or to eastern Brazil (Wagner et al. 1999). Regardless of the origin of S. capsicoides, it is not considered to be invasive in Florida. Native and exotic ranges for the six species are indicated in Table 2.

Table 2.

Native ranges of each of the five invasive Solanum spp. and current locations of establishment. (Information from Langeland and Craddock-Burks 1998, USDA/ARS 2008)

Control Measures

Prior to taking action to control a suspected invasive plant, verify that the plant is an invasive and not a native species. Species verification can be obtained from a local Florida Cooperative Extension Service office (http://solutionsforyourlife.ufl.edu/map/).

Chemical

Solanum tampicense. Herbicides that have shown the most promise in controlling this species include glyphosate, 2,4-D, and triclopyr. Seeds buried in the soil have been found to maintain their viability for as long as five years. As such, follow-up site scouting of treated areas and additional treatments of newly germinated plants may be necessary (Langeland and Stocker 2001).

Solanum viarum. Based on research conducted by Ferrell and Mullahey (2006), heavy infestations of tropical soda apple are best controlled by herbicides, such as Milestone or ForeFront. Aminopyralid is the active ingredient for both of these. Field research has shown that herbicides containing this particular active ingredient have been successful at not only postemergence control of tropical soda apple, but preemergence control of germinating seedlings more than six months after the initial application.

The following application rates for each herbicide are label rates for rangeland/pasture/open space with dense infestations: 1) Milestone, 5-7 oz./acre in at least 20 gallons of water per acre; 2) ForeFront R&P, 2-2.6 pints/acre in at least 20 gallons of water per acre.

A mowing regiment is not required when using these herbicides, but best results are obtained with the use of a non-ionic surfactant (0.25% v/v) in the spray mix. Herbicides effective for spot spraying include Remedy or Forefront, mixed at a 0.5% solution, or Milestone at 0.5 to 0.8 oz. per 2.5 gal. (15-20 ml per 2.5 gal). Consider adding 0.25% non-ionic surfactant and a color marker to the herbicide solution to help identify plants that have been treated. It is also recommended that application of spray is before budding/early flowering if possible. For more, see EDIS Publication SSAGR77, Tropical Soda Apple: Biology, Ecology and Management of a Noxious Weed in Florida, http://edis.ifas.ufl.edu/UW097.

A triclopyr formulation labeled for tropical soda apple is Remedy Ultra. Mowing is required to obtain best control of tropical soda apple in Florida when using this herbicide. Old infestations and/or newly germinating patches must be mowed regularly (every 50-60 days through April) to control budding and flowering. A broadcast treatment of 1 quart in 40 gallons of water/acre is recommended 50-60 days after the April mowing (late May-June). Follow-up with spot treatments (1-1 ½ gallons of Remedy Ultra in 100 gallons of total spray mixture) of remaining plants or newly germinated plants.

Solanum jamaicense/Solanum diphyllum. No research has been conducted on chemical control methods for either of these plants. Control methods developed for tropical soda apple (Solanum viarum) may be tried (see above) on these plants.

Solanum torvum. Control of turkeyberry has been achieved chemically on the Hawaiian Islands, where the plant has been found to be susceptible to translocated herbicides, such as glyphosate (Swarbrick 1997).

Biological

Solanum viarum. In early 2003, the South American beetle, Gratiana boliviana (Coleoptera: Chrysomelidae) was released in Florida for biological control of tropical soda apple. Since then, more than 250,000 beetles have been released in 42 counties in Florida. In addition, this beetle has been released in Georgia, Alabama, South Carolina, and Texas. The beetles are well established in Florida and cause considerable damage to tropical soda apple populations. In many cases, the beetles provide sufficient control and no additional control tactics are not required (Diaz et al. 2013).

Wunderlin, R. P. and B. F. Hanson. Atlas of Florida vascular plants. 2008. Institute for Systematic Botany, University of South Florida. Available at http://www.plantatlas.usf.edu/.

Footnotes

1.

This document is SS AGR 312, one of a series of the Agronomy Department, UF/IFAS Extension. Original publication date December 2008. Reviewed April 2011. Revised February 2014. Visit the EDIS website at http://edis.ifas.ufl.edu.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.